Final answer:
To test Boyle's law, the volume of a gas should be changed while measuring pressure at a constant temperature to observe the inverse proportionality between pressure and volume. So, the correct option is C.
Step-by-step explanation:
To test Boyle's law, we must change the volume of a gas and measure its pressure at constant temperature. Boyle's law states that for a given amount of gas at a constant temperature, the volume is inversely proportional to the pressure. This means that as the volume increases, the pressure decreases, and vice versa. This relationship can be represented mathematically by the equation P1V1 = P2V2, where P1 and V1 are the initial pressure and volume, and P2 and V2 are the final pressure and volume of the gas, with the temperature held constant.
The correct answer to the student's question would then be A) Temperature, since it is imperative to keep the temperature constant to accurately test the relationship between pressure and volume according to Boyle's law.